Diffuser having distribution element for providing part-flow

ABSTRACT

The invention relates to a gas turbine, for energy generation, with a compressor, arranged coaxially to a rotor, mounted such as to rotate, for the compression of an inlet gaseous fluid, at least partly serving for combustion of a fuel in a subsequent annular combustion chamber, with generation of a hot working medium, with an annular diffuser arranged coaxially to the rotor, between the compressor and the annular combustion chamber, for distribution and deflection of the fluid, whereby a part of the fluid is diverted as cooling fluid for the turbine stages after the combustion chamber, by means of a dividing element, arranged in the fluid flow. According to the invention, a compact diffuser and an economical gas turbine with an improved flow for the diversion of cooling air may be achieved, whereby the annular dividing element, arranged coaxially to the rotor, comprises at least one opening, facing the fluid flow and the dividing element is supported on the diffuser, by means of several hollow rib-like support elements, by means of which the cooling fluid, diverted through the opening, is first directed towards the rotor.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. Ser. No. 10/568,735, now U.S.Pat No. 7,574,864 filed on Feb. 17, 2006. This application is the USNational Stage of International Application No. PCT/EP2004/007947, filedJul. 16, 2004 and claims the benefit thereof. The InternationalApplication claims the benefits of European Patent application No.03018566.4 EP filed Aug. 18, 2003. All of the applications areincorporated by reference herein in their entirety.

FIELD OF THE INVENTION

The invention relates to a gas turbine in accordance with the claims andto a diffuser in accordance with the claims.

BACKGROUND OF THE INVENTION

DE 196 39 623 has disclosed a gas turbine for power generation having acompressor and an annular combustion chamber. A diffuser, which divertsthe compressed air provided by the compressor at the annular compressoroutlet in the direction of the burner arranged at the end side of theannular combustion chamber, is arranged between the compressor and theannular combustion chamber. For this purpose, the diffuser hasflow-guiding contours as well as a metal diverter sheet which isC-shaped in cross section and is secured by a holder crossing the flowpassage. Furthermore, a plurality of stationary removal tubesdistributed over the circumference are arranged in the diffuser,coaxially with respect to the rotor, for removing cooling air, whichremoval tubes remove cooling air at the compressor outlet and pass it tothe turbine stages of the gas turbine.

The holder for the C-shaped metal diverter sheet constitutes an obstacleblocking the flow passage formed by the diffuser. The arrangement of theremoval tubes also interferes with the air which is flowing in thediffuser and is passed to the burners. This can give rise to flowlosses. Furthermore, the tubes, which are distributed over thecircumference, have to have a minimum diameter required to ensure thatsufficient cooling air is provided for the turbine stages, so that notonly the compressed air which flows out of the center of the compressoroutlet but also the compressed air at the edge of the compressor outletis removed.

Furthermore, FR2706533 has disclosed a diffuser for a turbomachine, inwhich a part-stream is removed in the diffuser in order to set a cabinpressure, to deice the body of the machine or to start the engine of anaircraft. A wedge-shaped distribution element, which initially dividesthe compressor end air flow into two part-streams, is arranged in thewidening flow passage of the diffuser. Then, a third part-stream isremoved from the inner part-stream through an opening arranged behindthe tip of the distribution element. This third part-stream is routedoutward through the hollow ribs which support the distribution elementagainst the outer wall. The third part-stream removed in this way isthen used for the above-mentioned purposes. In a further configuration,the diffuser which is known from FR2706533 has an inner and outer ribssupporting the distribution element. The inner ribs are in this caseprovided with an opening for decoupling the part-flow, through whichopening the third part-flow that is to be decoupled can enter the cavityin the rib.

Since the part-flow removed in this way is used for deicing or, forexample, to set the cabin pressure, the demands imposed on the air flowin terms of degree of contamination, pressure and temperature arerelatively low.

By contrast, relatively high demands are imposed on the cooling air forthe turbine blades and vanes of a stationary gas turbine, in order onthe one hand to achieve a particularly high efficiency and on the otherhand to avoid or reduce blockages or cross-sectional narrowings ofimpingement cooling openings or film cooling holes caused by particledeposits.

SUMMARY OF THE INVENTION

Therefore, the object of the present invention is to provide a compactdiffuser with a partial air removal and a gas turbine having a diffuserof this type, which allows improved removal, in terms of fluid dynamics,of a part-flow used as cooling fluid for turbine blades and vanes.Furthermore, the part-flow needs to satisfy the demands relating to thedegree of contamination, pressure and temperature required for use ascooling fluid in a gas turbine.

The object relating to the gas turbine is achieved by the features ofthe claims. Advantageous configurations are given in the claims.

The solution with regard to the gas turbine provides that to decouple apart-stream that can be used as cooling fluid, the opening is providedon the leading edge, facing the flow, of the distribution element (35)in the form of an annular gap opening (49) in the central region betweenthe outer wall and the inner wall. The distribution of the compressedfluid takes place in a space-saving diffuser, which allows the coolingfluid for turbine stages to be removed in a manner which is favorable interms of flow and causes little turbulence and loss. At the same time,it is possible for the remaining fluid to be passed onward in afavorable manner in the direction of its subsequent areas of use, theannular combustion chamber walls. The distributed fluid streams crossone another without being significantly impeded and without generatingflow losses, since the supporting elements are provided with astreamlined profile.

If possible, a particularly clean and cool cooling fluid is usuallyemployed. (Suspended) particles contained in the cooling fluid can bedeposited at the impingement cooling openings of impingement-cooledcomponents, such as for example turbine blades or vanes, which areexposed to a hot gas, and in the worst possible scenario even blockthese openings.

On account of the swirl in the fluid which is present at the compressoroutlet and in the annular flow passage, (suspended) particles which ithas been impossible to filter out by mechanical means seek to movetoward the radially inner and outer edges of the flow passage. Likewise,higher temperatures and a lower pressure in the fluid are present at theradially inner and outer edges of the flow passage than in the centerlying between them. Consequently, the annular opening is arranged atprecisely the position in the diffuser at which the fluid which is mostsuitable for the cooling of the turbine stages is flowing. As a result,the fluid which is most suitable for cooling automatically flows intothe distribution element, forming a dynamic pressure, and is therebyseparated from the remaining fluid, which is less suitable for turbinecooling. The remaining fluid, which is subsequently used for combustion,is warmer than the decoupled cooling fluid and is at a lower pressure.

The coaxial annular gap opening causes the fluid to be decoupled ascooling fluid over the entire circumference of the annular distributionelement. Accordingly, the annular gap can be made narrower than thediameter of the removal tubes known from the prior art. In this way,only the coolest, cleanest fluid provided with the highest pressure isdecoupled as cooling fluid downstream of the compressor outlet ordiffuser inlet.

In an advantageous configuration, the distribution element is reinforcedand strengthened by ribs which are provided in the annular gap, run inthe axial direction and are distributed over the circumference of theannular gap. At the same time, these ribs serve as guide elements in thedistribution element for the cooling fluid which has already beendecoupled, so that it is routed in the direction of the supportingelement. It is therefore advantageous for the annular gap opening to besegmented along the circumference.

The walls which form the flow passage are already diverging in theportion of the flow passage which the distribution element is connectedupstream of. This increases the pressure in the fluid, which has apositive effect on the pressure of the decoupled cooling fluid.

If the annular distribution element is designed in a wedge shape bymeans of two walls and is arranged centrally between the two divergingwalls of the diffuser, so that in each case one wall of it and theopposite wall of the diffuser in each case form an annular part-passagefor the fluid, it is possible for the fluid intended for combustion of afuel to be divided into two part-streams of approximately equal size.The radially inner part-stream of the fluid can then still be used tocool the radially inner annular combustion chamber wall before it isused for combustion, and the part-stream of the fluid which is routedradially outward can be used to cool the radially outer annularcombustion chamber wall.

A particularly low-loss flow profile for the two part-streams can beachieved if the two part-passages have a substantially constant crosssection of flow over their flow length.

For reliable securing of the distribution element and for low-losscrossing of the decoupled cooling fluid through the radially innerpart-stream, the hollow supporting elements which route the coolingfluid in the interior are supported against the inner wall located onthe radially inner side. This allows the cooling fluid which has beendecoupled or removed by the distribution element in the center of thefluid flow to be diverted in the direction of the rotor with low losses.

The decoupled cooling fluid can be routed to the turbine unit in aparticularly simple way if it is routed radially inward by thesupporting element in order to be made available to the turbine stagesin a manner which is favorable in terms of fluid dynamics. For thispurpose, the cavity in the supporting element is in communication withan annular passage which is located further radially inward, is arrangedbetween the combustion chamber and the rotor and can pass the coolingfluid on to the turbines.

The fluid is expediently compressor air. A particularly cool cooling aircan be made available to the turbine stages if a tube with a nozzle runsthrough the cavity in the outer supporting elements, which nozzle opensout downstream of the opening, as seen in the direction of flow, and bymeans of which a liquid for generating heat of evaporation can beinjected into the cooling fluid stream. As a result, less cooling air isrequired, with the result that the opening can be made narrower andcooling air can be saved. Likewise, the diffuser and the distributionelement can be made more compact. The cooling air saving likewise leadsto an increase in the efficiency of the gas turbine.

It is expediently possible for a tube to extend through the cavity inthe outer supporting elements, which tube opens out in a passage whichis arranged in the distribution element and is flow-connected to theradially inner part-passage, so that a fuel can be introduced into thepart-passage. An inexpensive option is to use water as the liquid.

The object relating to the diffuser is achieved by the features of theclaims. The associated advantages correspond to those explained in thestatements given above.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is explained with reference to a drawing, in which:

FIG. 1 shows a diffuser with a distribution element arranged between thecompressor outlet and the annular combustion chamber,

FIG. 2 shows part of a segmented distribution element, and

FIG. 3 shows a partial longitudinal section through a gas turbine.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 3 shows a gas turbine 1 with a rotor 5 which is mounted such thatit can rotate about an axis of rotation 3. Along the rotor 5, the gasturbine 1 has a compressor 7, an annular combustion chamber 9 and aturbine 13, which is formed by four successive turbine stages. Aplurality of burners 11 are provided at the annular combustion chamber9, distributed over its circumference.

The compressor 7 draws in ambient air, compresses it and transfers it toa downstream diffuser 15, which is secured to the annular combustionchamber end of the compressor 7. The compressed air is distributed inthe diffuser 15. The majority of the air is routed along the annularcombustion chamber 9 for cooling purposes then mixed with a fuel, afterwhich it is burnt by means of the burners 11 in the annular combustionspace 17 to form a hot working medium 19. In the turbine 13, the workingmedium 19 flows past guide vanes 23 and rotor blades 25 in the hot-gasduct 21. As it does so, the working medium 19 expands at the rotorblades 25 secured to the rotor 5, so as to drive these blades. Therotational energy, which can be tapped off at the rotor 5, is used todrive an electrical generator.

FIG. 1 shows the annular diffuser 15 arranged between compressor 7 andannular combustion chamber 9 in detail. From a diffuser inlet 27, thediffuser 15 initially extends in the axial direction toward the annularcombustion chamber 9. A flow passage 29 is delimited by an inner wall 31located on the radially inner side and an outer wall 33 located on theradially outer side. The two walls 31, 33 diverge in the direction offlow of the fluid F.

As the flow passage 29 continues, an annular distribution element 35that is wedge-shaped in cross section is arranged in the diffuser 15,coaxially with respect to the rotor 5. The distribution element 35 has awall 37 which lies opposite the inner wall 31 located on the radiallyinner side and a wall 39 which lies opposite the outer wall 33 locatedon the radially outer side. The wall 37, together with the inner wall 31located on the radially inner side, forms a part-passage 45 for apart-stream 41. A further part-passage 47 for a further part-stream 43is delimited by the wall 39 and the outer wall 33 located on theradially outer side.

At its leading edge 48 facing the flow of fluid F, the annulardistribution element 35 has an annular gap opening 49.

Upper supporting elements 53, which are of rib-like and streamlinedconfiguration, extend between the outer wall 33 located on the radiallyouter side and the wall 39. Similarly shaped lower supporting elements55 extend between the wall 37 and the inner wall 31 located on theradially inner side. The annular distribution element 35 is positionedand held in the annular diffuser 15 by means of the supporting elements53, 55. The supporting elements 53, 55 are each of hollow design. Thelower supporting elements 55 are flow-connected to the annular gapelement 49, on the one hand, and to the annular passage 57 thatcoaxially surrounds the rotor 5, on the other hand.

A water tube 59, which ends in the distribution element 35 downstream ofthe annular gap opening 49, as seen in the direction of flow, can befitted radially from the outside through the upper supporting element53. An injection nozzle 63 is secured to that end of the water pipe 59which faces the distribution element 35. At the opposite end, the waterpipe 59 is connected to a water source.

A further fuel pipe 61, which passes through the upper supportingelement 53, extends into the distribution element 35, where it is incommunication with a passage which opens out into the first part-passage45. A fuel B can be fed to the fuel pipe 61. While the gas turbine 1 isoperating, air which has been compressed by the compressor 7 flows asfluid F through the diffuser inlet 27 into the diffuser 15. Thewedge-shaped distribution element 35 divides the fluid F into twopart-streams 41, 43 of approximately equal size and a middle part-stream51. The part-stream 51, in the region of the leading edge 48, flows intothe annular gap passage 49 and is thereby removed or decoupled from thefluid flow.

The first part-stream 41 is routed to the annular combustion chamberwall located on the radially inner side. From there, the part-stream 41flows along the annular combustion chamber wall, cooling the latter, andis then mixed with a fuel in the burner 11. The mixture is then burnt inthe annular combustion chamber 9 to form the hot working medium 19.

The part-stream 43 which flows within the further part-passage 47, afterit has emerged from the diffuser 15, is routed to the radially outerannular combustion chamber wall, and from there is routed onward intothe burner 11, where it is likewise mixed with a fuel and then burnt inthe combustion space 17 to form the hot working medium 19.

The middle part-stream 51 flows into the distribution element 35 and isdiverted in the direction of the lower supporting elements 55. Fromthere, it flows through the hollow supporting elements 55 in thedirection of the rotor 5 and opens out into an annular passage 57. Then,this part-stream 51, as cooling fluid, is routed to the turbine stagesparallel to the axis of rotation 3 and used there to cool the guidevanes 23 and rotor blades 25.

The middle part-stream 51 has the most favorable properties for use as acooling fluid. In the flow passage 29, the compressor air iscontaminated to a greater extent with particles in particular in thevicinity of the radially inner and outer walls 31, 33 of the diffuser15, whereas the middle flow located in between is as far as possibledevoid of particles. In addition, the lowest pressure combined with thehighest pressure is likewise present in the same region. Therefore, thispart of the flow is used to cool the blades and vanes arranged in theturbine.

The temperature of the middle part-stream 51 can be additionally reducedby water H₂O being injected downstream of the annular gap opening 49through the water pipe 59. The nozzle 63 atomizes the water H₂O to formsmall beads of water, so that it can evaporate more easily, with theresult that it extracts heat from the part-stream 51. As a result, thequantity of cooling fluid required is reduced further, and the openingwhich extends in the radial direction, in particular the annular gapopening 49, can as a result be made even narrower.

The fuel which mixes with the part-stream 41 is injected through thefuel pipe 61. During the cooling of the radially inner annularcombustion chamber wall, the mixture is heated, which has a positiveeffect on the NOx content in the working medium 19 during combustion,i.e. the NOx content is reduced. As seen in the direction of flow, thefuel B is supplied well downstream of the distribution of the fluid F inthe downstream region of the part-passage 45. This prevents backflow ofthe fuel B and therefore prevents it from mixing with the part-stream51.

FIG. 2 shows the distribution element 35 as seen in the direction offlow. The distribution element 35 is supported against the inner walllocated on the radially inner side by means of the lower supportingelements 55 and against the outer wall 33 located on the radially outerside, which is not shown here, by means of the upper supporting elements53. The walls 37, 39, together with the opposite walls 31, 33 of thediffuser 15, in each case form a part-passage 45, 47. On its side facingthe compressor 7, the distribution element 35 has an annular gap opening49, which is segmented by means of radially extending ribs 65.

From the compressor 7, the fluid (F) in the diffuser 15 flows in thedirection of the distribution element 35, where it is divided into threepart-streams 41, 43, 51.

The middle part-stream 51 flows into the annular gap opening 49 and isdiverted in the direction of the rotor 5 by the inner contour of thehollow distribution element 35. It then flows through the hollow lowersupporting ribs 55 and after that is fed into the annular passage 57,from where the part-stream 51 is routed in the axial direction to theturbine stages and is then used to cool the guide vanes and rotorblades, which are exposed to hot gas, so that their impingement and filmcooling openings can provide the specified cooling air for a longerperiod of time on account of the reduced contamination of the coolingair.

The invention claimed is:
 1. A diffuser for extracting cooling air forturbine stages of a gas turbine, comprising: an inner wall forming aradially inner side of the diffuser; an outer wall forming a radiallyouter side of the diffuser that provides a flow passage having an inletand an outlet where the inner and outer walls increasingly diverge alongthe direction of fluid flow; an annular passage bypassing extractedcooling air around a combustion chamber and to the turbine stages,wherein the annular passage is located radially inward of the innerwall; an annular distribution element arranged coaxially along alongitudinal axis and between the inner and outer walls of the diffuserhaving a centrally located opening that creates a cooling airpart-stream of the compressor discharge fluid flow, where thedistribution element opening is arranged on a leading edge of thedistribution element and forms an annular opening in a central regionbetween the outer wall and the inner wall; and a plurality of hollowlower and upper supporting elements arranged between the inner and outerwalls, respectively, of the diffuser and the annular distributionelement wherein at least one of the hollow lower supporting elements isin fluid communication with the annular passage.
 2. The diffuser asclaimed in claim 1, wherein the distribution element creates a radiallyoutward and a radially inward streams that coaxially surround thecentrally located cooling air part stream.
 3. The diffuser as claimed inclaim 1, wherein a tube including a nozzle is routed through one of theplurality of hollow upper supporting elements, where the nozzle isarranged within the annular opening of the distribution element andinjects a cooling fluid into the cooling air part-stream.
 4. Thediffuser as claimed in claim 3, wherein the cooling fluid is water. 5.The diffuser as claimed in claim 2, wherein a wall of the distributionelement is located opposite the inner wall to form a radially innerpart-passage and a fuel supply tube extends through a hollow uppersupporting element of the plurality of hollow upper supporting elementsand wherein the fuel supply tube connects to a passage in thedistribution element connected to the radially inner part-passage thatdefines the radially inward stream and introduces a fuel into theradially inner part-passage.
 6. The diffuser as claimed in claim 1,wherein the annular opening is segmented along a circumference of theannular distribution element.
 7. The diffuser as claimed in claim 1,wherein the annular distribution element is arranged centrally betweenthe two diverging walls of the diffuser and has a wedge shape defined bytwo walls such that each distribution element wall and the adjacentdiffuser wall form two annular part-passages for the fluid.
 8. Thediffuser as claimed in claim 7, wherein each of the two annularpart-passages have a substantially constant cross section over each flowlength of the two annular part-passages.
 9. The diffuser as claimed inclaim 1, wherein the hollow lower supporting elements route a coolingfluid through an interior of the hollow lower supporting elements andare supported against the diffuser inner wall.
 10. The diffuser asclaimed in claim 1, wherein the cooling air part-stream is routed towarda rotor of the gas turbine by the hollow lower supporting elements.